Environmental Erosion Research

fa بررسی اثر عمق خیسی بر توان برآورد رواناب و رسوب با استفاده از معادله اصلاح شده ویلیامز (منطقه مورد مطالعه: دامنه قلات شهرکرد) Investigation of the Effect of Wetting Depth on Estimation of Runoff and Sediment Production Capacity Using the Modified Williams Equation (Study Area: Qalat Shahrekord Range) مدلسازی و تحلیل زمانی و مکانی رخداد انواع مختلف فرسایش محیطی مستخرج از پایان‌نامه / رساله / طرح پژوهشی عمق خیسی، مقدار آبی است که در خاک نفوذ و لایه داخلی آن را مرطوب میکند و متغیری مهم در کاربردهایی مانند تولید رواناب و برآورد عملکرد رسوب است. این متغیر در برخی موارد در علم هیدرولوژیکی، جایگزینی برای نفوذ است و از آن به عنوان عاملی مهم در فرایندهای فرسایش خاک استفاده میشود. ارزیابی اثر عمق خیسی بر تولید رسوب و رواناب ناشی از فرسایش آبی با استفاده از بارانساز، در کشور و در دنیا  موضوع جدیدی است و پژوهش‌‌های متعددی در این زمینه انجام نشدهاست. بنابراین اهمیت و ضرورت این تحقیق، برآورد رسوب معلق با اضافه کردن متغیر عمق خیسی به مدل منطقهای است. هدف از این تحقیق نیز بررسی اثر عمق خیسی بر توان تولید رواناب و رسوب با استفاده از معادله اصلاح شده ویلیامز است. در این مطالعه میدانی، از یک شبیهساز باران مجهز به سیستمهای قطرهای نصب شده روی یک قطعه آزمایشی در دامنه کوه استفاده شد و منظور از آن، تولید بارندگی با  دو شدت 45 و 60 میلیمتر در ساعت در سه شیب 10، 20 و 30 درصد با سه تکرار بود. سپس رواناب و رسوب به دست آمده از هر پلات، در فواصل زمانی ده دقیقه‌ای در بطری‌های مخصوص جمعآوری و به آزمایشگاه منتقل شد. در ادامه، مقدار رسوب تولید شده در پایان هر بارش، وزن و برای هر پلات محاسبه شد. برای اندازهگیری عمق خیسی با استفاده از میلهای بافت نازک درجهبندی شده، میزان عمق خیسشدگی هر ده دقیقه یکبار به صورت قطری با سه تکرار در داخل پلات صورت گرفت. از ضریب تبیین (R2) و معیار نش ـ ساتکلیف (Nse) نیز به عنوان معیارهای عملکرد رسوب برای مدل استفاده شد. نتایج نشان داد که در ارزیابی نتـایج در شبیه‌سازی میزان رسوب، ضریب نش ـ ساتکلیف و ضریب تبیین به عنوان دو مورد از پرکاربردترین شاخصها، مقدار 88/0 Nse= و 88/0R2= را از خود نشان دادند. نتایج حاصل از برآورد میزان رسوب معلق در مراحل واسنجی (81/0 Nse= و 81/0R2=) و اعتبارسنجی (81/0Nse=  و 81/0R2=)، برای منطقه مورد مطالعه بسیار مناسب بود.   1- Introduction Depth to wet front is generally considered as the amount of water which penetrates into soil and wets the internal soil layer. This is an important variable especially in applications such as runoff generation and sediment yield estimation. This variable in some cases is used as a hydrological science in the form of a proxy for infiltration as an important factor in soil erosion processes. The importance and necessity of this research is estimating the performance of suspended sediment by adding the wetting depth variable to the regional model. The aim of this study was to investigate the effect of wetting depth on runoff and sediment production capacity by using the modified Williams equation. 2- Methodology In this field study, a rain simulator equipped with drip systems installed on a test site on a mountain slope to produce rainfall with intensities of 45 and 60 mm per hour on three slopes of 10, 20 and 30% was used with three replications. Adjacent to the experimental plots, soil surface depth was used to determine the physical and chemical properties of the soil, including soil texture, lime percentage, organic matter, initial moisture and aggregate stability. After setting the artificial sprinkler on the experimental plot, runoff and sediment obtained from each plot were collected in special bottles at 10-minute intervals and transferred to the laboratory. Then the amount of sediment produced at the end of each precipitation was weighed and calculated for each plot. Then, to measure the wetting depth using thin tissue rods, the wetting depth was measured every 10 minutes in diameter with 3 repetitions inside the plot. Explanation coefficient (R2) and Nash-Sutcliffe return (Nse) were used as sediment yield criteria for the model. 3- Results According to the results obtained in the study area and the efficiency coefficient, before adding the wetting depth parameter, the effect of precipitation intensity on sediment indicates a significant difference. The Nash coefficients at intensities of 45 and 60 mm/h are 0.84 and 0.63%, respectively, while the Nash coefficient for the combined intensities (total) of 45- and 60 mm/h is 0.55. Due to the low Nash coefficient in the Williams equation, for investigating the wetting depth on the amount of sediment, the Williams equation was modified. Based on the results in the study area, the relationship between wetting depth and the amount of suspended sediment in the mentioned intensities and slopes through the equation of Qs=(qe×qpe)0/32×S0/28×1/17dp×DA2/89 was obtained. Sediment performance has a non-linear and inverse relationship with wetting depth at the desired intensities and slopes, and also with the parameters of slope, runoff volume, runoff peak discharge and area. The results showed that the extent that increasing the slope, runoff, runoff peak and area leads to increasing the amount of sediment, and increasing the wetting depth reduces the amount of suspended sediment. The calibration and validation results of estimating the amount of suspended sediment in the developed model showed the value of Nse= 0.81; R2 = 0.81. 4- Discussion & Conclusions This study investigated the effect of wetting depth on runoff and sediment production capacity in the field at slopes of 10, 20 and 30% with rainfall intensities of 45 and <st1:metricconverter productid="60 mm" w:st="on">60 mm</st1:metricconverter>/h using the modified Williams equation. In the present case without considering the wetting depth variable, the results showed that at intensities of 45 and <st1:metricconverter productid="60 mm" w:st="on">60 mm</st1:metricconverter>/h, the amount of sediment and runoff increases by increasing the slope. This is because the shear energy poured on the soil by raindrops has produced runoff and sediment. But by combining rainfall intensities of 45 and <st1:metricconverter productid="60 mm" w:st="on">60 mm</st1:metricconverter> per hour, the amount of Nash coefficient decreased. One of the reasons for this is the increase in the diameter of raindrops and also the increase in the number of droplets that hit the soil surface. Although increasing the intensity of rainfall in most soils increases sediment by increasing runoff, it can sometimes reduce sediment efficiency by reducing sediment due to the spatial homogeneity of the slope of the soil surface layer. Addition of slope and wetting depth parameter, which is due to the amount of infiltration that moistens the soil around the bottom layers, is one of the factors that affect the production of sediment. The results of evaluating the efficiency of the regional model showed that the equation obtained for the region fits well with the observational data to the extent that the coefficient of explanation of fitted lines on the data increased by adding the wetting depth variable. There is an inverse exponential relationship between the amount of leached sediment and the wetting depth. Performance coefficient indices such as sedimentation coefficient and explanation coefficient, as two of the most widely used indicators to evaluate the results in the simulation of the amount of sediment, showed the value of Nse = 0.88 and R2 = 0.88. The results of estimating the amount of suspended sediment in the calibration (Nse = 0.81; R2 = 0.81) and validation (Nse = 0.81; R2 = 0.81) stages were very suitable for the study area. شدت بارندگی, شیب, رسوب معلق, فرسایش خاک, عمق خیسی. Rainfall intensity, Slope, Soil erosion, Suspended sediment, Wet depth. 105 121 http://magazine.hormozgan.ac.ir/browse.php?a_code=A-10-264-3&slc_lang=fa&sid=1 Mehdi Pajouhesh مهدی پژوهش pajouhesh.mehdi@sku.ac.ir 10031947532846007080 10031947532846007080 Yes Natural Resources Department, Faculty of Agriculture & Natural Resources, University of Shahrekord, Chaharmahal va bakhtyari گروه مهندسی منابع طبیعی، دانشکده کشاورزی و منابع طبیعی، دانشگاه هرمزگان، بندرعباس Shiva Parsi شیوا پارسی sh.parsi96@gmail.com 10031947532846007081 10031947532846007081 No Natural Resources Department, Faculty of Agriculture & Natural Resources, University of Shahrekord, Chaharmahal va bakhtyari گروه مهندسی طبیعت، دانشکده منابع طبیعی و علوم زمین، دانشگاه شهرکرد Nasrin Gharahi نسرین قرهی na_gharahi@yahoo.co.uk 10031947532846007082 10031947532846007082 No Natural Resources Department, Faculty of Agriculture & Natural Resources, University of Shahrekord, Chaharmahal va bakhtyari گروه مهندسی محیط زیست، دانشکده منابع طبیعی و علوم زمین، دانشگاه شهرکرد Khodayar Abdollahi خدایار عبدالهی abdollahikh@gmail.com 10031947532846007083 10031947532846007083 No Natural Resources Department, Faculty of Agriculture & Natural Resources, University of Shahrekord, Chaharmahal va bakhtyari گروه مهندسی طبیعت، دانشکده منابع طبیعی و علوم زمین، دانشگاه شهر کرد